title: How to distinguish between the annihilation and the creation of optical vortices.
abstract: Optical vortices are always created or annihilated as vortex dipoles-pairs with opposite topological charge. Here a quantity, consisting of the transverse first and second derivatives of the optical field, is derived with which one can distinguish between vortex dipole annihilation and creation events. Analytical and numerical examples are provided as a demonstration of the method.
authors.forename: Filippus S
authors.initials: FS
authors.lastname: Roux